Impulsing apparatus for signaling systems



June 22, 1943. I EfMATOUSEK IMPULSE APPARATUS FOR SIGNALING SYSTEMS Filed Dec. 6, 1941 INVENTOR. EDWARD MATOUSEK ATTORNEYS mm, 9 m 25 5 5E 5 3E z I 8 02mm x e i 0 1 2 g; 3 5 M225 2 2 o e\ QHKNS I mo )m 4 mzz m2: 21 .O E

. ow mozwjm Patented June 22, 1943 IMPULSIN G APPARATUS FOR SIGNALING SYSTEMS :Edward ;Matousek, Berwyn, 111., assignor to Associated Electric Laboratories, Inc., Chicago, 111., a. corporation of Delaware Application December 6, 1341, Serial No. 421,878

8 Claims.

The present invention relates to signaling apparatus and, more particularly, to improvements in impulse responsive equipment of the character used in automatic telephone systems.

It isan object of the present invention to provide an improved and exceedingly simple arrangement for preventing the one of the impulse-controlled relays of an impulse-controlled device, such, for example, as a selector or repeater, from releasing when the device is respond ng to impulses transmitted thereto over a. high resistance line.

According to another-object of the invention, the release period of the relay is enhanced by utilizing an electron discharge tube to sustain the current fiowthrough the winding of the relay each time the circuit "for energizing this winding is opened by an associated int-pulsing relay.

Inaccordance with another object of themvention, the electron discharge tube is also arranged to minimize sparking at the .impulsin'g relay contacts which are connected to Control the operatin circuit for the relay having the accentuated release period.

The invention, hothas to its organizationand method of operation, together with further obiects and advantages thereof, will best be understood by reference to the specification taken in connection with the accompanying drawing in which the single figure illustrates the invention as incorporated in an impulse-controlled selector of an automatic telephone system.

Referring now more particularly to the drawing. the system there illustrated comprises impulse-controlled switching equipment for setting up connections between a plurality crimes In, l I, etc, which respectively extend to the substations A, B. etc. This automatic switching equipment includes a line switch individual to the line 10, cor-responding switches-individual to the other subscriber lines of the system,a plurality of impulse-controlled selectors including the illustrated selector 20, and "a plurality of impulsecontrolled connectors including the schematicaliv illustrated connector 25, through which access is obtained to desired called lines. Each of the line switches of the system maybe of any desired commercial construction, although prefer-' ably theseswi'tches are of the well-known rotary type. Similarly, the-connectors may be of any desired commercial construction and arrangement, although prefer-ably are of the wellknown Strowger type.

The selectors included in the system are identical in construction and Wiring arrangement. Briefly considered, the selector 29 comprises a Strowger switching mechanism having its contact -field divided into ten levels of bank contacts which have the -wipers 36, 3| and 3'2 associated therewith. The mechanism further comprises the usual vertical and rotary magnets 33 and 34 which are operative in conjunction with their associated ratchet and pawl mechanisms, not shown, to impart vertical and rotary movement to the wipers 30, 3| and 32. The mechanism is also equipped with a release magnet -35 which, when energized, permits the wipers 31!, 3! and 32 to be returnedto rotary and vertical normal; vertical off-normal springs "36, 31 and 38 which are respectively operated whenthe Wipers 30, 3! and 32 are stepped to the first vertical off-normal positions thereof; and cam springs 39, 49 and M which are respectively operated when the indicated wipers are rotated to the eleventh rotary off-normal positions thereof. In addition to theStrowger switching mechanism just described, the selector 20 comprises a line relay R NE, a slow-acting hold relay R! H) which is normally connected across the exchange battery in series with an electron discharge tube 45., a slowacting transfer relay EH20, a test relay R-l'fiil, and a switch-through relay RIM. It will be .understood that all of the control relays and operating magnets of the various switches provided in theillustrated system are supplied with energizing current from a-common direct current source which may comprise the usual exchange battery. This hatterymay have a voltage of approximately 50 volts, which voltage is maintained within close limits. The electron tube is preferably of the gas-filled-discharge type, this tube being characterized by a breakdown .or ionizing voltage which is somewhat greater than the voltage of the exchange battery, and by operating and extinction voltages which are also somewhat greater than the voltage of the exchange battery. As will be explained more fully hereinafter, this tube serves to enhance the release period of therelease relay RI l0 andalso to prevent sparking at thecontacts |0| of the impulsing relay Rlili! during the transmission of tor-Mandthe connectori2'5Jtotheli-ne H. When the call is initiated at the substation A, a, calling loop circuit is established by way of the line III which causes the line switch I to operate in a well-known manner, sequentially to test the idle or busy condition of the selectors to which it has access. Assuming that the selector 2!] is the first idle selector selected by the line switch I5, the operation of the latter switch is arrested and the calling loop circuit is extended to the indicated selector, incident to the engagement of the line switch wipers with the contacts terminating the conductors of the trunk incoming to the selector 20. Incident to the switch-through operation of the line switch [5, the calling loop circuit is extended through the contacts I4I, I43 and I22 to include the two windings of the impulsing relay R533 in series with the exchange battery. In operating, this relay opens its contacts I02 to interrupt an incomplete circuit for transmitting impulses to the parallel-connected windings of the transfer relay RI23 and the vertical magnet 33. At its contacts IIlI, the relay RIIIII completes a circuit through the contacts I41 for energizing the winding of the release relay RI Ill. At its contacts IilI, the relay RIIlIl also completes a path including the contacts I41 for short-circuiting the electrodes of the discharge tube 45.

The relay RI Iii, upon operating, closes its contacts I II to complete an obvious path for impressing ground potential upon the test conductor c, thereby to maintain the line switch I5 in its operated position and to provide a guard path which prevents the selector from being seized through the other line switches to which it is accessible. At its contacts III, the relay RI I0 also prepares a locking circuit for the switch-through relay Ri iil and. completes a circuit through the offnormal springs 36 for energizing the upper Winding of the transfer relay RIZII. At its contacts I I2, the relay RI Iii prepares the operating circuit for the test relay RI30. At its contacts II3, the relay RI it prepares the above-mentioned circuit for transmitting current pulses to the parallelconnected windings of the relay RIZII and the vertical magnet 33. At its contacts I I4, the relay RI It opens a point in the circuit for energizing the release magnet 35. At its contacts I I5, the relay RI Ii] prepares the operating circuits for the switch-through relay RIM] and the rotary magnet 34.

The transfer relay RIZB, upon operating, closes its contacts I2! and opens its contacts I22, thereby to include the dial tone generator, not shown, and the cam springs 39 in the loop circuit which extends between the selector 20 and the calling substation A. In response to this operation, dial tone signaling current is transmitted over the calling loop circuit to signal the calling subscriber at the substation A that the dialing operation may be started. At its contacts I23, the relay At its contacts I26, the relay RI20 opens a point in the prepared operating circuit for the rotary magnet 34.

When the dial tone signal is received at the calling substation A, the calling subscriber may dial the first digit of the directory number designating the desired substation B. For purposes of;

explanation it may be assumed that this digit comprises eight impulses. During the open-circuit period of the first impulse, the relay Rlllll restores and opens its contacts IOI to interrupt the above-traced operating circuit for the release relay RI I0. At its contacts I02, the relay RI III] completes the above-mentioned circuit for energizing the lower winding of the transfer relay RI2Il and the vertical magnet 33, this circuit extending from ground by way of the contacts I41, I02, H3 and I23, and the parallel-connected windings of RI20 and the vertical magnet 33, to battery. In operating, the vertical magnet 33 elevates the wipers 30, SI and 32 one step, wherein they are positioned opposite the first level of bank contacts in the associated contact field. After this stepping operation is completed, and at the end of the open-circuit period of the first impulse, the line relay RIM! is again energized and opens its contacts I32 to interrupt the circuit for energizing the parallel-connected windings of the relay RIZi) and the vertical magnet 33. At its contacts IOI, the relay RIGO recompletes the operating circuit for the release relay RI I0. During each succeeding impulse of the digit-the operations just described are repeated, the vertical magnet 33 operating to elevate the wipers 30, 3| and 32 one step in response to each current pulse transmitted thereto. It will be understood, therefore, that at the end of the digit the enumerated wipers are left standing opposite the level of bank contacts in which are terminated the trunk conductors of the connectors having access to the desired line I I.

Incident to the first vertical step of the wipers 30, 3I and 32, the vertical ofi-normal springs 36 are disengaged to deenergize the upper winding of the transfer relay RI2II. Since the lower winding of this relay receives a current pulse during each impulse transmitted to the selector 20, and is of the slow-to-release type, it remains operated until shortly after the digit is ended. Also incident to the first vertical step of the selector wipers, the oiT-normal springs 31 are closed to prepare the operating circuit for the release magnet 35 and the off-normal springs 38 are closed to prepare the operating circuit for the rotary magnet 34.

At the end of the first digit, the impulsing and release relays RIIII) and RI I0 are held operated to cause the deenergization and release of thetrarlsfer relay RI20. Upon restoring, this, relay opens its contacts I2I and closes its contacts I22, thereby to exclude the dial tone generator from the loop circuit which extends to the calling substation. Thus the dial tone signal being reproduced at this substation is terminated. At its contacts I23, the relay RI2I] opens another point in the circuit for energizing its lower winding in parallel with the vertical magnet 33. At its contacts I24, the relay RI20 opens a point in the path for impressing ground potential upon the wiper 3I. At its contacts I25, the relay RI2Il further prepares the operating circuit for the release magnet 35. At its contacts I 26, the relay R completes the prepared operating circuit for the rotary magnet 34, this circuit extending from ground by way of the contacts H5, I32 and I48, the offnormal springs 38, the contacts 34a, the winding of the magnet '34 and the contacts I25, to battery. When energized in this circuit, the magnet 34 operates to rotate the wipers 30, 35 and 32 into engagement with the contacts forming the first contact set of the selected eighth level. The succeeding operations depend upon the idle or busy condition of the first connector thus selected in the selected group of connectors. If this connector is busy, the test conductor thereof is'marked with ground potential so that the winding of the test relay RIM] is short-circuited over a path which includes the test wiper 32 and the contacts II2. Ac cordingly, this relay is prevented from operating. On the other hand, if the first connector of the selected group is idle, the test conductor thereof is marked with negative battery potential to energize the test relay RI3IJ in a circuit which includes the test wiper 32 and the contacts I III. In such case the test relay Hi3!) immediately operates to arrest the trunk hunting operation in the manner explained below.

In operating, the rotary magnet 34 also opens its contacts 34a to deenergize its own winding. Upon releasing this magnet recloses its contacts 34a to again energize its operating circuit and, hence, reoperates to step the wipers 30, 3| and 32 into engagement with the contacts terminating the trunk conductors of the second connector in the selected group. If this connector also tests busy, the rotary magnet 34 is again released and reoperated to advance the selector wipers a third step. The rotary step by step movement of these wipers continues until all of the connectors in the selected group have been tested and found to be busy, or until an idle connector in the group is found. Assuming that all of the connectors of the selected group are busy, the wipers 30, 3| and 32 are operated to their eleventh rotary off-normal positions, at which time the cam springs 4| are closed to complete an alternative circuit for energizing the transfer relay RIZII, this circuit extending from ground by way of the contacts II5, I32 and I48, the ofl-normal springs 38, the cam springs 4|, and the upper winding of RI20 to battery. Also, incident to the eleventh rotary step of the selector wipers, the cam springs 39 are opened further to interrupt the above-described dial tone signaling circuit and the cam springs 4|] are closed to prepare a busy signaling circuit. Upon reoperating, the relay R120 opens its contacts I26 to interrupt the above-traced operating circuit for the rotary magnet 34 and thus prevent further o eration of this magnet. At its contacts I 24, the relay RI 20 reprepares the above-mentioned path f r impressing ground potential upon the winer 3|.

At its contact IN, the relay RIZII serially includes the busy tone generator, not shown, and the cam springs 40 in the loop circu t extending to the calling substation, whereby the usual busy tone signal is reproduced at this substation to indicate that a connection with the desired. line cannot be obtained.

When the connection is released at the calling substation A, the three relays RIIIII, RI II] and control an overflow meter, not shown, thereby.

to register the all-busy condition of the selected group of connectors. In releasing, the release relay RIIII also opens its contacts III to disconnect the test conductor 200 from ground and thus initiate the release 'of the line switch I5. When this conductor is disconnected from ground, the selector20 is marked as idle in the bank contacts of the line switches to which it is accessible. Upon restoring, the release relay RI'III also opens its contacts I I5 to deenergize the transfer relay RI ZII. The latter relay, upon restoring, closes its contacts I23 to complete the prepared operating circuit for the release ma net 35, this circuit extending from ground by Way of the contacts I4], I02, H4 and I25, the vertical oIf-norma1 springs 31, and the winding of the magnet 35 to battery. When thus energized, the magnet 35 attracts its associated holding pawl, permitting the wipers 33, 3| and 32 to be returned to rotary and vertical normal. Incident to the release of the selector switching mechanism, the oif-normal springs 31 are disengaged to deenergize the release magnet 35; the off-normal springs 38 are disengaged further to interrupt the operating circuit for the rotary magnet 34; the on-normal springs 33 are engaged to reprepare the operating circuit for the transfer relay R'IZII; the cam springs 4| are opened further to interrupt the alternative operating circuit for the transfer relay RI2I3; the cam springs 39 are closed and the cam springs 43 are opened. Following the release of the transfer relay BIZ!) and the release of the Strowger switching mechanism in the selector 20, this switch is fully restored to normal.

Assuming now that the connector 25 is the first idle connector of the selected group, the trunk hunting operation of the selector 20 is arrested when the wipers of this selector are positioned to engage the contacts terminating the conductors of the trunk extending to this connector. At this time, the test relay RI39 is energized from the exchange battery as connected to the test wiper 32 over the test lead of the trunk extending to the connector 25. In operating, this relay opens its contacts I32 to interrupt the above-traced operating circuit for the rotary magnet 34 and thus prevent further rotary movement of the wipers 30, 3! and 32. At its contacts I3I, the relay RIM completes a circuit through the contacts II5 for energizing the switch-through relay RIM.

Upon operating, the relay RIM closes its contacts I45 to connect the test conductor 280 through the test wiper 32 to the test conductor of the trunk extending to the connector 25, whereby this connector is marked as busy in the bank contacts of the other selectors and a locking circuit is prepared for the switch-through relay. At its contacts I48, the relay RIM] opens another point in the operating circuit for the rotary magnet 34. At its contacts I48, the relay Rlfii! locks to ground through the engaged contacts II I of the release relay RI III, and prepares an alternative locking circuit for itself which includes the test conductor of the trunk extending to the connector 25. At its contacts M5, the relay RI49 also short-circuits the test relay RI3II over a path which includes the contacts III and H2. When thus short-circuited the relay RI30 is rendered slow-to-release. At its c011- tacts I'l, the relay RIM opens a point in the previously traced circuits for energizing the vertical magnet 33, the release magnet 35, and the transfer relay RI20. At its contacts I I! and I43, the relay RM!) excludes the windings of the impulsing relay R109 from the calling loop circuit. At its contacts I 42 and I44, the relay RI 40 extends the calling loop circuit to the seized connector 25. In response to the latter operation the line and hold relays conventionally embodied in the connector 25- operate to connect the test wiper 32 to ground over a path which includes the test conductor of the trunk extending to this connector. Thus locking circuits are provided for the switch-through relay RIM) and the switch-through relay of the line switch I15.

Shortly following the seizure of the connector 25 in the manner just explained, the deenergized impulsing relay RIM opens its contacts IOI to deenergize the release relay RIIU. The relay RI II upon restoring, opens its contacts H2 and III to interrupt the path short-circuiting the Winding of the test relay RI30. At its contacts N4, the relay RI I prepares the operating circuit for the release magnet 35. At its contacts H5, the relay RI I0 opens another point in the operating circuit for the rotary magnet 34. At its contacts III and H2, the relay RI III also disconnects the test conductor 200 from ground in the selector 20, whereby the release of this selector is transferred to the control of the line and hold relays embodied in the seized connector 25. Following the release of the three relays RIIIU, RI I0 and Rl3ll in themanner just described, no further operation of the selector 2!] occurs until the connection is released at the calling end thereof.

The manner in which the connection may be extended through the connector 25 to the desired line ii, and the desired talking circuit set up between the calling and called substations when the call is answered, is entirely conventional and will be readily understood by those skilled in the art. Briefly to consider these operations, it is pointed out that upon the selection of the line I I this line is tested to determine the idle or busy condition thereof. If the selected line tests busy the usual. busy tone signal is returned over the calling end of the connection to inform the calling subscriber that the desired connection cannot be obtained. On the other hand, if the selected line tests idle, ringing current is transmitted thereover to energize the signal device provided at the called substation B and the usual ring-back tone signal is transmitted to the calling subscriber to indicate that the called substation is being rung. These signaling operations are arrested and the desired talking circuit is completed when the receiver. provided at the called substation is removed from its supporting hook or cradle to complete an answering loop circuit between this substation and the connector 25. When the connection is clearedout at the calling end thereof, the connector 25 is released in an entirely conventional manner. Incident to the release of this switch the test wiper 312 is disconnected from ground to deenergize the relay EH39 and the operated switch-through .relay of the line switch I5. The switch-through relay RIM], upon restoring, closes its contacts I41 to complete the previously traced operating circuit for the release magnet 35. When thus energized the magnet 35 attracts its holding pawl, permitting the wiper carriage structure of the Strowger switching mechanism in the selector 2!] to be returned to rotary and vertical normal. Following the release of this mechanism the selector 20 is fully restored to normal.

As indicated above, the present invention relates to the arrangement of the discharge tube @5, whereby this tube functions to enhance the release period of the slow-acting relay RI III. In

this regard it may be noted that when the impulsing relay RIM] is controlled by impulses transmitted thereto over a calling line having a high series resistance, the response of the relay to the received impulses may be somewhat sluggish. For example, if a standard impulsing rate is used in the transmission ofimpulses over a calling loop circuit characterized by a series resistance of approximately 1500 ohms, the opencircuit period of each impulse, i. e., that period during which the impulsing relay RIM is restored, may exceed the release period of the slowacting relay RI I0 unless provisions are made for further enhancing the slow-to-release character-' istic of the latter relay. On the other hand, when a calling loop circuit of low series resistance is used in the transmission of impulses to the selector 29, the response of the relay RISE] to the opening and closing of the loop circuit is sufliciently fast to preclude the release of the relay RI I0.

In considering the manner in which the discharge tube enhances the release period of the slow-acting relay RI Ill, it will'be'understood that since the breakdown or striking voltage of this tube is in excess of the voltage across the termi-j nals of the exchange battery, the tube is normally deionized. with the relay RIM operated, following seizure of the selector 26 and before the switch-through operation occurs, the tube 45 is shunted by the contacts IllI. When, however, the impulsing relay RIM! is deenergized during the open-circuit period of a received impulse, it opens its contacts ID! to interrupt this shunting path. At this instant, the flux traversing the'magnetic circuit of the field structure forming a part of the relay Hi It, produces a counter E. M. F. in the winding of this relay which increases the voltage, across the electrodes of the discharge tube 35. More specifically, this counter voltage, which is eifectively added to the voltage of the exchange battery, raises the voltage across the electrodes of the tube 45 to a value in excess of the character.- istic breakdown or striking voltage of the tube. Accordingly, the discharge tube is ionized to sustain the current flow through the winding of the relay RI It so long as the voltage thereacross is in excess of the characteristic extinction voltage thereof. Immediately the tube 45 is ionizedthe voltage across the electrodes thereof drops to the characteristic operating voltage of thetube. As indicated above, the extinction voltage is also greater than the exchange battery voltage. Ac

cordingly, when the transient current, occasioned by the counter E. M. F. built up in the winding of the relay RI Ill and utilized to sustain the ener-, gization of this relay, decays to a certain predetermined value such thatthe voltage drop across the electrodes of the tube 45 is reduced below the characteristic extinction voltage of the tube, the tube is deionized to interrupt the only available circuit for passing current through the winding of the relay RI III.

The instant that the current path through t e tube 45 is thus broken, a second but smaller kick in the voltage thereacross is produced by the counter E. M. F. developed in the winding of the relay RI Ill. If the resulting voltage rise across the electrodes of the tube exceeds the characteristic breakdown voltage thereof, the' tube may again be ionized and the operations described above repeated, thereby furtherto enhance the above brief explanation of'the manner in which It will also be apparent that the tube 45 functions to increase the release period of the relay RHO, it will be understood that the extent of this increase is determined by the inductive and resistive constants of the winding of the relay EHO, and the characteristic breakdown, operating and extinction voltages of the tube 45 when an exchange battery of standard voltage is used as a current supply source.

By a proper selection of these constants the release period of the relay RI I0 may be enhanced by an amount suflicient to increase the length of subscriber lines over which the selector 20 may be directively controlled by dial impulses.

As previously noted, the discharge tube 45 has the added function of minimizing sparking at the break contacts IOI, incident to the release of the impulsing relay RIOU. In this regard it will be understood that in the absence of this tube, the voltage of the exchange battery, assisted by the counter E, M. F. developed in the winding of the relay Rllll at the instant the operating circuit for this relay is broken, is impressed across the separating contacts lfll to sustain the are developed thereacross. With the arrangement illustrated, however, the discharge tube 45 acts as a voltage limiter to prevent the voltage across the separating contacts lili from rising beyond a predetermined value. Thus immediately the tube 45 is ionized the drop across the electrodes of this tube, and hence the separating contacts lill, is limited to the characteristic operating voltage of the tube. The remaining portion of the available voltage drop appears as an impedance drop across the winding of the relay RI l0. Thus the voltage which tends to sustain the arc is materially less than the voltage which would act to sustain the arc across these contacts if the discharge tube 45 were not provided in the circuit.

Although the improved impulse-controlled network as equipped with the discharge tube 45 for performing the functions briefly referred to above has been illustrated as being provided in an automatic selector switch, it will be understood that this network is capable of being used in many other applications. For example, the network may be employed without modification in the connector 25, or in an inter-office trunk repeater. It may also be used in an impulsecontrolled register and in many other applications which will be apparent to those skilled in the art.

While one embodiment of the invention has been disclosed, it will be understood that various modifications may be made therein which are within the true spirit and scope of the invention.

What is claimed is:

1. In a telephone system which includes a plurality of lines; an impulse-controlled selector having access to said lines and including a release relay operative to prevent the release of said selector during the transmission of impulses thereto, an impulse responsive line relay operative to direct the operation of said selector in the selection of one of said lines, an electron discharge device connected in circuit with the winding of said release relay and operative to delay the release of said release relay for a short interval after said release relay is deenergized,

and means comprising said line relay for controlling the energization and deenergization of said release relay,

2. In a telephone system which includes a plurality of lines, an impulse-controlled selector having access to said lines and including a release relay, a circuit including a source of current and the winding of said relay, an electron discharge device serially included in said circuit and operative to sustain for a short interval the current flow through said winding each time said circuit is opened, and means comprising an im--' pulse repeating relay for intermittently completing said circuit and for directing the operation of said selector to select one of said lines.

3. In an impulse-controlled device, a release relay including a Winding, a circuit for energizing said winding, an electron discharge tube operative to sustain for a short interval the current flow through said winding each time said circuit is opened, and means comprising an impulsing relay for opening and closing said circuit when impulses are transmitted to said device.

4. In an impulse-controlled device, a release relay including a winding, a source of current, an electron discharge tube, a circuit serially including said winding, said source and said tube, and means comprising an impulsing relay for shunting said tube from said circuit when said device is conditioned for operation and for intermittently opening the shunting path when impulses are transmitted to said device, said tube being operative to sustain for a short interval the current flow through said Winding each time said shunting path is opened.

5. In an impulse-controlled device, a release relay including a winding, a source of current, a circuit for energizing said winding from said source, a gaseous discharge tube having a breakdown voltage which is greater than the voltage of said source but less than the combined voltage of said source and the counter voltage developed across said winding when said circuit is opened, and means comprising an impulsing relay for completing said circuit and for including said tube in said circuit each time said circuit is opened, whereby current flow through said winding is sustained for a short interval after said circuit is opened.

6. In a relay network, a relay including a winding, a circuit for energizing said winding, means for closing and opening said circuit, and means comprising an electron discharge device included in said circuit for delaying the release of said relay when said circuit is opened.

7. In a relay network, a relay including a winding, a circuit for energizing said winding, contacts for closing and opening said circuit, and means comprising an electron discharge device shunting said contacts for delaying the release of said relay when said contacts are opened.

8. In a relay network, a relay including a. winding, a circuit for energizing said winding, contacts for closing and opening said circuit, and means comprising an electron discharge device connected in shunt with said contacts for minimizing sparking at said contacts and for delay ing the release of said relay when said contacts are opened.

EDWARD MATOUSEK. 

